Better Linux Sound Management With ALSA - page 2

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February 29, 2008

By
Carla Schroder

You're going to need alsa-base and alsa-utils. Suppose you have a single sound card on your system; either a PCI sound card or onboard sound. This is easy. Just fire up alsamixer to configure it, as Figure 1 shows. That's for my onboard AC97-based chipset. (As always, lspci will show you what's on your system.) alsamixer only displays supported functions. The top-left captions tell you a lot of useful information: your sound card and chipset, which set of functions you're viewing, and the values for the highlighted setting. The default view is Playback, like in Figure 1. There are three views: Playback, Capture, and All. Hit the Tab key to toggle between them. Figure 2 shows the Capture screen.

Basic navigation and settings are easy: go back and forth with the right and left arrow keys, and hit the Escape key to close. The little boxes with MM in them means that function is muted, or disabled. Toggle the M key to mute/unmute. 00 means zero volume, so use the up and down arrow keys to adjust it. When there are two channels you can adjust each one independently, which you can see in the Master setting in Figure 1. Q increases the left channel, and Z decreases. E and C control the right channel. In the Capture screen, use the spacebar to select the active recording device.

Most of the settings are self-explanatory, but there is oft confusion over Master and PCM. Master controls your playback volume. A PCM device is like a virtual soundcard; this is the bit that converts analog sound to digital. It can be either software or hardware. Your Linux sound applications need the PCM channel. So you usually need both of these active to enable playback.